This invention relates to in situ recovery of shale oil, and more particularly to a thermally insulated bulkhead for sealing an access drift adjacent a hot portion of an in situ oil shale retort.
The presence of large deposits of oil shale in the Rocky Mountain region of the United States has given rise to extensive efforts to develop methods for recovering shale oil from kerogen in the oil shale deposits. It should be noted that the term "oil shale" as used in the industry is in fact a misnomer; it is neither shale, nor does it contain oil. It is a sedimentary formation comprising marlstone deposit with layers containing an organic polymer called "kerogen", which upon heating, decomposes to produce liquid and gaseous products. It is the formation containing kerogen that is called "oil shale" herein, and the liquid hydrocarbon product is called "shale oil".
A number of methods have been proposed for processing oil shale which involve either first mining the kerogen-bearing shale and processing the shale on the ground surface, or processing the shale in situ. The latter approach is preferable from the standpoint of environmental impact, inasmuch as the treated shale remains in place, reducing the chance of surface contamination and the requirement for disposal of solid wastes.
The recovery of liquid and gaseous products from oil shale deposits has been described in several patents, such as U.S. Pat. Nos. 3,661,423; 4,043,595; 4,043,596; 4,043,597; and 4,043,598, which are incorporated herein by this reference. These patents describe in situ recovery of liquid and gaseous hydrocarbon materials from a subterranean formation containing oil shale, wherein such formation is fragmented to form a stationary, fragmented permeable body or mass of formation particles containing oil shale within the formation, referred to herein as an in situ oil shale retort.
Hot retorting gases are passed through the fragmented mass to convert kerogen contained in the oil shale to liquid and gaseous products, thereby producing retorted oil shale. One method of supplying hot retorting gases used for converting kerogen contained in the oil shale, as described in U.S. Pat. No. 3,661,423, includes establishing a combustion zone in the fragmented mass and introducing an oxygen-supplying gaseous combustion zone feed into the fragmented mass to advance the combustion zone through the fragmented mass. In the combustion zone, oxygen in the combustion zone feed is depleted by reaction with hot carbonaceous materials to product heat, combustion gas, and combusted oil shale. By the continued introduction of the combustion zone feed into the fragmented mass, the combustion zone is advanced through the fragmented mass.
The combustion gas and the portion of the combustion zone feed that does not take part in the combustion process pass through the fragmented mass on the advancing side of the combustion zone. This heats the oil shale in a retorting zone to a temperature sufficient to produce kerogen decomposition, called "retorting", in the oil shale. The kerogen decomposes into gaseous and liquid products, including gaseous and liquid hydrocarbon products, and into a residual solid carbonaceous material.
The liquid hydrocarbon products, together with water produced in or added to the fragmented mass, are collected at the bottom of the fragmented mass. An off gas also is withdrawn from the bottom of the fragmented mass. The off gas contains combustion gas, including carbon dioxide generated in the combustion zone, gaseous products produced in the retorting zone, carbon dioxide from carbonate decomposition, and any gaseous combustion zone feed that does not take part in the combustion process. The products of retorting are referred to herein as liquid and gaseous products.
The off gas produced during retorting can contain carbon monoxide and sulfur compounds such as hydrogen sulfide. Hydrogen sulfide and carbon monoxide are extremely toxic gases. For this reason it is desirable to seal an access drift which is in fluid communication with the fragmented mass so that workers in adjacent underground workings are isolated from the off gas produced in the fragmented mass during retorting operations.
Retorting operations in the fragmented mass can generate hot combustion gases in an access drift adjacent a hot portion of the fragmented mass. The temperature of gases in such an access drift can be 1400.degree. F. or higher. It is desirable to provide a gas seal in such an access drift which can withstand such high temperatures without structural failure at least during the active life of the retort.